Inventors have long been concerned with devising penetration resistant panels to serve as doors for safes and vaults.
U.S. Pat. No. 63,046 granted Mar. 19, 1867 to E. M. Hendrickson for "Burglar-Proof-Safe" discloses a safe wall containing soft metal wire bent in spiral form and intended to break a drill penetrating the panel.
J. M. Ewing in his U.S. Pat. No. 100,741 granted Mar. 15, 1870 for "Burglar Proof Safe" disclosed a panel composed of chains interlinked or interwoven with each other. In theory the burglar's tools were turned aside by the yielding chain links.
U.S. Pat. No. 2,773,459 granted Dec. 11, 1956 to P. S. Sechy for "Protective Wall for Use Against Radiation and Explosive Forces" discloses a wall structure composed of a plurality of corrugated metal sheets, resilient material and concrete.
R. E. Hollis, Sr. disclosed the use of overlapping, spot welded wavy steel wires in his U.S. Pat. No. 3,969,563 granted Jul. 13, 1976 for "Protection Wall Structure".
The fact is any of these wall structures can be penetrated by the tools and explosives available to the modern burglar or espionage agent if the perpetrators are given sufficient time.